The present invention relates to a charged particle beam apparatus using a charged particle beam such as an electron beam or ion beam. More particularly, it relates to a charged particle beam apparatus and a dimension measuring method which are preferable for measuring the dimension of a specified domain with a high accuracy even if height differences exist within the field-of-view.
In charged particle beam apparatuses representative of which is a scanning electron microscope, a narrowly converged charged particle beam is scanned on a sample, thereby acquiring desired information (e.g., sample image) from the sample. In the charged particle beam apparatuses like this, implementation of the high resolution has been progressing year by year. Of these charged particle beam apparatuses, in electron beam apparatuses in particular, diffraction phenomenon of the electrons is conspicuous and dominant. As a result, a decrease in the focal depth in accompaniment with the high-resolution implementation is unavoidable in principle. Meanwhile, under the circumstances like this, it is now required to perform a high-reliability dimension measurement with a higher accuracy. However, in a situation in particular where a plurality of measurement positions accompany height differences with respect to the electron beam, it becomes difficult to perform the high-reliability dimension measurement.
Conventionally, in order to automatically perform the dimension measurement, the following method has been generally used: Namely, a condition for allowing the best focus to be achieved is found out from the entire contrast within the field-of-view including a dimension-measuring domain. Then, after setting the focus, the dimension of a predetermined domain is measured from a SEM image newly acquired based on this focusing condition. Also, as a technique for acquiring a deep focal-depth SEM image of a sample which accompanies asperities or height differences, a technique of acquiring a plurality of SEM images with different focuses has been disclosed in JP-A-2002-75263. In JP-A-2002-75263, the method has been disclosed which allows the deep focal-depth SEM image to be acquired by extracting best-focused image domains from these SEM images respectively and superimposing these image domains into the one piece of SEM image. Also, in JP-A-11-264726, the following method has been disclosed: Namely, the plurality of SEM images with the different focuses are acquired, and the dimension measurements are performed in length-measuring domains in the respective SEM images. Then, a measurement value whose variation in the measurement results acquired for the focus variations becomes the smallest is assumed as the dimension's true value.